A million taxpayers who need to submit a self-assessment tax return must do so by midnight on Saturday.
Those who fail to meet the deadline for online returns risk incurring a £100 fine.
A record 11 million people are required by their tax arrangements to submit a return.
Most now do so online and as that can be done from a computer at home, many leave it until the last moment.
Last year 700,000 missed the deadline, though Revenue and Customs accepted some excuses - such as a death in the family, serious illness or flooding.
Women on time
On deadline day last year, 557,000 people rushed to file in time.
Recent analysis by HMRC suggested that women were more likely to submit their tax returns on time than men.
For every 10,000 tax returns received last year from men, 394 were after the relevant deadlines, compared with 358 late returns from every 10,000 submitted by women.
Interest is charged on any tax paid late and those who still have not submitted the form by May face additional penalties fines of £10 a day.
It is already too late to send in paper tax returns for the 2013-14 tax year as that deadline passed on 31 October.
Those who have failed to register for online submissions have also missed the boat.